window.onload = function(){
	var nav = document.getElementById('nav');
	var li = nav.getElementsByTagName('li');
	var img = document.getElementById('imgs');
	var div = img.getElementsByTagName('div');
	for(var  i = 0 ; i < li.length;i++){
		li[i].index = i ;
		li[i].onmouseover = function(){
			for (var j = 0 ; j < li.length ;j++){
				li[j].className = '';
				div[j].className = 'banner'+(j+1);
		 	}
			this.className ='select';
			div[this.index].className += 'active' ;
		}
	}
}
